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The absorption spectra, excitation spectra, and emission spectra of Tb 3þ ∕Eu 3þ ions in LiYF 4 single crystals synthesized by an improved Bridgman method are measured. The emission spectra of several bands, mainly located at blue ∼487 nm (Tb: 5 D 4 → 7 F 6 ), yellowish green ∼542 nm (Tb: 5 D 4 → 7 F 5 ), and red ∼611 nm (Eu: 5 D 0 → 7 F 2 ) wavelengths, are observed under excitation by UV light. An ideal white light emission as a result of simultaneous combination of these emissions can be obtained from 1.11 mol% Tb 3þ and 0.9 mol% Eu 3þ co-doped LiYF 4 single crystals with chromaticity coordinates of x ¼ 0.3242, y ¼ 0.3389, color temperature T c ¼ 5878 K, color rendering index R a ¼ 77, and color quality scale Q a ¼ 75 under excitation of 384 nm light. The chromaticity coordinate, color rendering index, and color quality scale can be modified by the change of the concentration of rare-earth dopants and the excitation wavelength.

The Ho 3+ /Yb 3+ co-doped α-NaYF 4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient (70−90 • C/cm) of solid-liquid interface was adopted. Upconversion emissions at green ∼544 nm, red ∼657 and ∼751 nm were obtained under 980 nm laser diode excitation. The intensity at ∼544 nm was much stronger than those of ∼657 and ∼751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb 3+ concentration was about 8.08mol% when Ho 3+ concentration was hold at about 1.0mol%. The results showed that Ho 3+ /Yb 3+ doped α-NaYF 4 single crystal was a possible candidate upconversion material for the green solid-state laser.

Downconversion (DC) luminescence with emission at about 1000 nm under excitation of 448‐nm light in Ho3+/Yb3+ codoped α‐NaYF4 single crystal is realized. The crystal was grown by the Bridgman method using KF as an assisting flux in a NaF‐YF3 system. The energy‐transfer process and quantum cutting (QC) mechanisms are presented through the analysis of the spectra. The energy‐transfer processes of first‐ and second‐order cooperative DC are responsible for the increase of the emission intensity at 1000 nm, and it is the first‐order cooperative DC that is dominant for the DC process. When the Ho3+ concentration is fixed at about 0.8 mol%, the optimal concentration for ∼1000 nm emission is 3.02 mol% Yb3+ in the current research. The energy‐transfer efficiency and the total quantum efficiency are analyzed through the luminescence decay curves. The maximum quantum cutting efficiency approaches to 184.4% in α‐NaYF4 single crystals of 0.799 mol% Ho3+ and 15.15 mol% Yb3+. However, the emission intensity at 1000 nm decreases while the energy‐transfer efficiency from Ho3+ to Yb3+ increases, which may result from the fluorescence quenching between Ho3+ and Yb3+ ions, Yb3+ and Yb3+ ions.